The present invention relates to an image forming apparatus which forms an electrostatic latent image on a latent image carrier by using writing electrodes of a writing device, thereby forming the image.
In a conventional image forming apparatus such as an electrostatic copying machine and a printer, the surface of a photoreceptor (photosensitive member) is uniformly charged by a charging device and the charged surface is then exposed to light from an exposure device such as laser beam or LED light, whereby a latent image is written on the surface of the photoreceptor. Then, the latent image on the surface of the photoreceptor is developed by a developing device to form a developing powder image on the surface of the photoreceptor. The developing powder image is transferred to a receiving medium such as a paper, thereby forming the image.
In such conventional image forming apparatus, the exposure device as a writing device for electrostatic latent image comprises a laser beam generating device or a LED light generating device. Therefore, the entire image forming apparatus should be large and complex.
Therefore, an image forming apparatus has been proposed in Japanese Patent Publication No. S63-45104 (hereinafter, ""104B publication) which employs electrodes, as a writing device for forming an electrostatic latent image, to write an electrostatic latent image on a surface of a latent image carrier without using laser beams and LED lights.
The image forming apparatus disclosed in the ""104B publication is provided with a multistylus having a large number of needle electrodes. The needle electrodes are just arranged in contact with an inorganic glass layer on the surface of the latent image carrier. In accordance with an input signal for image information, voltages are selectively applied to corresponding ones of the needle electrodes of the multistylus, whereby the electrostatic latent image can be formed on the latent image carrier. Since the image forming apparatus according to the ""104B publication does not use an exposure device conventionally used as a writing device, the invention of this publication can provide an image forming apparatus which is relatively small in size and relatively simple in structure.
In addition, an image forming apparatus has been proposed in Japanese Unexamined Patent Publication No. H06-166206 (hereinafter, ""206A publication), comprising ion control electrodes which are disposed on a front end portion of an insulating substrate and are arranged in non-contact with a latent image carrier, wherein the ion control electrodes control ions generated by a corona discharger so as to write an electrostatic latent image on the latent image carrier. Since the image forming apparatus according to the ""206A publication also does not use an exposure device as a writing device, the invention of this publication can provide an image forming apparatus which is relatively small in size and relatively simple in structure.
However, in the image forming apparatus according to the ""104B publication, the large number of needle electrodes of the multistylus are just arranged in contact with the inorganic glass layer on the surface of the latent image carrier. It is difficult to keep the stable contact between the needle electrodes and the inorganic glass layer on the surface of the latent image carrier. Accordingly, it is difficult to stably apply charge to the surface of the latent image carrier. This means that it is hard to obtain a high quality image.
Moreover, it is unavoidable to employ an inorganic glass layer on the surface of the latent image carrier for protecting the surface of the latent image carrier from damage due to contacts of a large number of the needle electrodes. This makes the structure of the latent image carrier more complex. In addition, since the inorganic glass layer has quite well physical adsorbed water characteristic, moisture is easily adsorbed by the surface of the inorganic glass layer. Due to the moisture, the electrical conductivity of the glass surface is increased so that electrostatic charge on the latent image carrier should leak. Therefore, the image forming apparatus should be provided with a means for drying the surface of the latent image carrier with adsorbed moisture in order to prevent the apparatus from being affected by absorbed water. This not only makes the apparatus larger but also increases the number of parts, leading to problems of making the structure further complex and increasing the cost.
Since the large number of needle electrodes discharge, the apparatus has another problem that there is a high possibility of generation of ozone (O3). The presence of ozone may not only produce rusts on parts in the apparatus but also melt resin parts because ozone reacts with NOx to generate nitrous acid (HNO3). Again ozone may give an offensive smell. Therefore, the image forming apparatus should be provided with an ventilation system including a duct and an ozone filter which sufficiently exhausts ozone from the inside of the apparatus. This also not only makes the apparatus larger but also increases the number of parts, leading to problems of making the structure further complex and increasing the cost.
On the other hand, in the image forming apparatus according to the ""206A publication, ions produced by the corona discharger are controlled by the ion control electrodes. This means that the apparatus is structured not to directly inject electric charge to the latent image carrier. The invention of the ""206A publication has problems of not only making the image forming apparatus larger and but also making the structure complex. Since the application of charge is conducted by ions, it is difficult to stably write a latent image on the latent image carrier.
Further, since the generation of ions essentially generates ozone, there are problems similar to those described with regard to the image forming apparatus according to ""104B publication.
It is an object of the present invention to provide an image forming apparatus capable of more stably writing an electrostatic latent image and yet achieving reduction in size and reduction in the number of parts thereof so as to have more simple and low-priced structure.
It is another object of the present invention to provide an image forming apparatus capable of further preventing generation of ozone.
In order to achieve these objects, the present invention provides an image forming apparatus which comprises at least: a latent image carrier on which an electrostatic latent image is formed, a writing device for writing said electrostatic latent image on said latent image carrier, and a developing device for developing said electrostatic latent image on the latent image carrier, wherein said electrostatic latent image, written on said latent image carrier by said writing device, is developed by said developing device, thereby forming an image, and is characterized in that said writing device has writing electrodes for writing said electrostatic latent image on said latent image carrier and a flexible substrate for supporting said writing electrodes, wherein said writing electrodes are in contact with said latent image carrier with a small pressing force due to elasticity of said flexible substrate, and that each of said writing electrodes comprises a convexity projecting from said substrate toward said latent image carrier.
The present invention is characterized in that said each writing electrode is formed in any one of configurations including a portion of sphere, a circular column, a cone, a truncated cone, an elliptic column (column of which cross section is elliptic), an elliptic cone (cone of which cross section is elliptic), a truncated elliptic cone (truncated cone of which cross section is elliptic), an oval column (column of which cross section is oval), an oval cone (cone of which cross section is oval), a truncated oval cone (truncated cone of which cross section is oval), a triangle column, a triangle pyramid, a truncated triangle pyramid, a square column, a square pyramid, a truncated square pyramid, a polygonal column having five corners or more, a polygonal pyramid having five corners or more, and a truncated polygonal pyramid having five corners or more.
The present invention is further characterized in that at least said each writing electrode is coated with a protective layer.
The present invention is still characterized in that at least a portion of said each writing electrode confronting said latent image carrier is made of a material easily to wear.
The present invention is still further characterized in that said developing device is a developing device for developing said electrostatic latent image with developing powder consisting of a single component; by further comprising a transferring device for transferring a developing powder image on said latent image carrier, developed by said developing device, to a receiving medium; and in that residual developing powder left on said latent image carrier after transfer is adapted to be charged to have the same polarity as the original polarity of said developing powder consisting of a single component.
Further, the present invention is characterized in that a large number of microscopic particles are interposed at least between said writing electrodes and said latent image carrier to allow free rolling of said microscopic particles, wherein said microscopic particles are adapted to be charged at least to have the same polarity as the original polarity of said developing powder before developing of said electrostatic latent image.
Furthermore, the present invention is characterized by further comprising a charge control device for making said latent image carrier into a uniformly charged state, wherein residual developing powder left on said latent image carrier after transfer is adapted to be charged to have the same polarity as the original polarity of said developing powder consisting of a single component at the same time when said charge control device makes said latent image carrier into the uniformly charged state.
Moreover, the present invention is characterized in that said developing is reverse developing.
In the image forming apparatus of the present invention having the aforementioned structure, a convexity of each writing electrode is in contact with a latent image carrier so that the surface of the writing electrode is not entirely in contact with the latent image carrier, thereby allowing easy passing of foreign matters adhering to the surface of the latent image carrier and thus preventing the filming of the surface of the latent image carrier.
In addition, the writing electrodes are supported by a flexible substrate, thereby stabilizing the positions of the writing electrodes relative to the latent image carrier and thus stably and reliably conducting the application or removal of charge by the writing electrodes relative to the latent image carrier. Therefore, stable writing of an electrostatic latent image onto the latent image carrier is achieved, thus reliably obtaining a high quality image with high precision.
Since the writing electrodes can be securely kept in contact with the latent image carrier with a small pressing force by the flexible substrate, the gap (space) between the writing electrodes and the latent image carrier can be eliminated. No gap practically reduces the possibility that air existing in the gap is undesirably ionized, thereby further reducing the generation of ozone and enabling the formation of an electrostatic latent image with low potential. In addition, the latent image carrier can be prevented from being damaged by the writing electrodes, thus improving the durability of the latent image carrier.
Further, since the writing device employs only the writing electrodes without using a laser beam generating device or a LED light generating device which is large in size as conventionally used, the apparatus size can be reduced and the number of parts can also be reduced, thereby obtaining an image forming apparatus which is simple and low-price.
In the present invention, since the convexity of the writing electrode is allowed to be formed in various configurations, the writing electrode is flexible to be employed in various types of image forming apparatus. In particular, when the convexity of the writing electrode is formed in a portion of sphere, a cone, an elliptic cone, an oval cone, a triangle pyramid, a square pyramid, or a polygonal pyramid having five corners or more, the writing electrode and the latent image carrier are in point contact, thereby further securely allowing foreign matters adhering to the surface of the latent image carrier to pass through. When the convexity of the writing electrode is formed in a circular column, a truncated cone, an elliptic column, a truncated elliptic cone, an oval column, a truncated oval cone, a triangle column, a truncated triangle pyramid, a square column of which cross section is a parallelogram or a trapezoid, a truncated square pyramid of which cross section is a parallelogram or a trapezoid, a polygonal column (having five corners or more), and a truncated polygonal pyramid (having five corners or more), the writing electrode has side faces inclined against the feeding direction, whereby foreign matters adhering to the surface of the latent image carrier can easily pass through because the foreign matters easily slide along the inclined faces.
In the present invention, at least the writing electrodes are coated with the protective layers. The protective layers prevent wear of the writing electrodes and prevent foreign matters from adhering to the writing electrodes.
In the present invention, since the portion of the writing electrode confronting the latent image carrier is made of material easily to wear, the surface of the writing electrode should wear due to the contact relative to the latent image carrier so as to have a fresh surface so that the surface of the writing electrode can be kept fresh, thus preventing the filming of the writing electrode.
In the present invention, residual developing powder which is left on the latent image carrier after the transfer is charged to have the same polarity as the original polarity of the developing powder consisting of a single component. Therefore, the residual developing powder, placed on non-image portions of the latent image carrier and charged as mentioned above, can be moved to a developing roller during the developing, while the residual developing powder, placed on image portions of the latent image carrier and charge as mentioned above, still remains on the latent image carrier as developing powder for subsequent developing. That is, this apparatus can form an image in the cleaner-less cleaning method in which the developing of a latent image and the cleaning of the latent image carrier can be simultaneously conducted.
In the present invention, employment of the writing device achieves reduction in size and simplification of the structure of the image forming apparatus. In addition, since it is a cleaner-less image forming apparatus without a cleaning device, further simple structure can be achieved.
In the present invention, a large number of microscopic particles are interposed at least between the writing electrodes and the latent image carrier. With the aid of the microscopic particles, foreign matters adhering to the surface of the latent image carrier can easily pass through, thus preventing the filming on the surface of the latent image carrier and on the surfaces of the writing electrodes. In addition, Free rolling of the microscopic particles reduces the friction between the writing electrodes and the latent image carrier, leading to reduction in torque for rotating the latent image carrier.
Since the charge of the microscopic particles is adapted to be charged to have the same polarity as the original polarity of the developing power, consisting of a single component, of the developing device, the residual developing powder on non-image portions of the latent image carrier can be further effectively removed or collected by the microscopic particles, placed on the non-image portions of the latent image carrier and charged as mentioned above. Interposing the microscopic particles between the writing electrodes and the latent image carrier enables to eliminate the necessity of the charge control device, thereby further simplifying the structure of the image forming apparatus without cleaning device.
In the present invention, since residual developing powder which is left on the latent image carrier after the transfer is charged to have the same polarity as the original polarity thereof at the same time when the latent image carrier is uniformly charged by the charge control device, application of charge to the residual developing powder can be easily conducted.
In the present invention, the developing is conducted by the reverse developing method. In this reverse developing method, the residual developing powder can be uniformed to have the same polarity of the developing powder during the process of uniformly charging the latent image carrier, thereby further easily and effectively conducting the cleaning at the same time of developing.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.